Smooth pursuit is a voluntary eye movement that is used to view objects as they move. Although physiologists have studied many aspects of voluntary saccade control, most work on the neural control of pursuit has treated this system as if it responds reflexively to retinal-image motion. The pursuit system of primates is a sophisticated ocular movement system that has evolved to allow it to predict when and where an object will move, and to decide whether or not to pursue that object. The focus of the current grant period is to understand how the cortical eye fields cooperate to control voluntary smooth pursuit eye movements. Aims are to: 1. Compare the strength of predictive and retinal-image signals used by the cortical eye fields to execute a pursuit eye movement 2. Determine how the cortical eye fields interact to cancel a pursuit movement. 3. Determine how the decision is made to execute or cancel a pursuit movement. The results of these experiments should contribute to our knowledge of how the cortex moves the eyes to effectively view moving objects in the natural scene. The results of this work should provide basic data to facilitate diagnosis and treatment of disorders of vision such as strabismus and amblyopia, and to develop prosthetic devices to aid people who suffer from these disorders.